The IMS (IP multimedia subsystem) customized ring back tone service is a type of service that is customized by a calling user or a called user and provides the calling user with a piece of melodious music, a phrase of greeting, a picture or a video image, etc. instead of the ordinarily beeping ring back tone. Accordingly, if the calling user or the called user is a user of customized ring back tone, the calling user hears or sees the personalized customized ring back tone customized by the user when dialing the telephone number of the called user. The IMS customized ring tone service is a type of service that is customized by a calling user or a called user and provides the called user with a piece of melodious music, a phrase of greeting, a picture or a video image, etc. instead of the ordinarily beeping ringing tone when the called user receives a call from the calling user. Accordingly, if the calling user or the called user is a user of customized ring tone, the called user hears or sees the personalized customized ring tone customized by the user when receiving a telephone call from the calling user.
Existing IMS customized ring back tones can be implemented by the mode of early session. With regard to the IMS customized ring tones, the early session mode is also defined as one of the implementation modes. During the process of the same session, if the calling user and the called user both customize the customized ring back tone and the customized ring tone services, and the customized ring back tone and the customized ring tone are both implemented by the early session mode, during the process of signaling transmission, two content-dispositions which are simultaneously contained in the message body of a signaling message are both the SDPs, Session Description Protocol, of the early session. Under such circumstances, it is impossible for the customized ring back tone server to identify which one thereof is the SDP answer for the customized ring back tone service sent from the calling terminal, and it is hence impossible to perform media negotiation with the calling terminal to play the customized ring back tone; it is also impossible for the customized ring tone server to identify which one thereof is the SDP answer for the customized ring tone service sent from the called terminal, and it is hence impossible to perform media negotiation with the called terminal to play the customized ring tone.